diff --git a/system/src/Grav/Framework/Cache/AbstractCache.php b/system/src/Grav/Framework/Cache/AbstractCache.php
index de749a1c6..82ba8cc9d 100644
--- a/system/src/Grav/Framework/Cache/AbstractCache.php
+++ b/system/src/Grav/Framework/Cache/AbstractCache.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\Cache
  *
diff --git a/system/src/Grav/Framework/Cache/Adapter/ChainCache.php b/system/src/Grav/Framework/Cache/Adapter/ChainCache.php
index 041b676f2..d66c4eeb1 100644
--- a/system/src/Grav/Framework/Cache/Adapter/ChainCache.php
+++ b/system/src/Grav/Framework/Cache/Adapter/ChainCache.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\Cache
  *
@@ -48,7 +49,7 @@ class ChainCache extends AbstractCache
                 throw new InvalidArgumentException(
                     sprintf(
                         "The class '%s' does not implement the '%s' interface",
-                        get_class($cache),
+                        \get_class($cache),
                         CacheInterface::class
                     )
                 );
@@ -56,7 +57,7 @@ class ChainCache extends AbstractCache
         }
 
         $this->caches = array_values($caches);
-        $this->count = count($caches);
+        $this->count = \count($caches);
     }
 
     /**
diff --git a/system/src/Grav/Framework/Cache/Adapter/DoctrineCache.php b/system/src/Grav/Framework/Cache/Adapter/DoctrineCache.php
index 3a69c1ff9..5282bbdf0 100644
--- a/system/src/Grav/Framework/Cache/Adapter/DoctrineCache.php
+++ b/system/src/Grav/Framework/Cache/Adapter/DoctrineCache.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\Cache
  *
@@ -10,7 +11,6 @@ namespace Grav\Framework\Cache\Adapter;
 
 use Doctrine\Common\Cache\CacheProvider;
 use Grav\Framework\Cache\AbstractCache;
-use Grav\Framework\Cache\Exception\InvalidArgumentException;
 
 /**
  * Cache class for PSR-16 compatible "Simple Cache" implementation using Doctrine Cache backend.
@@ -100,16 +100,6 @@ class DoctrineCache extends AbstractCache
      */
     public function doDeleteMultiple($keys)
     {
-        // TODO: Remove when Doctrine Cache has been updated to support the feature.
-        if (!method_exists($this->driver, 'deleteMultiple')) {
-            $success = true;
-            foreach ($keys as $key) {
-                $success = $this->delete($key) && $success;
-            }
-
-            return $success;
-        }
-
         return $this->driver->deleteMultiple($keys);
     }
 
diff --git a/system/src/Grav/Framework/Cache/Adapter/FileCache.php b/system/src/Grav/Framework/Cache/Adapter/FileCache.php
index 389b626e1..799051d60 100644
--- a/system/src/Grav/Framework/Cache/Adapter/FileCache.php
+++ b/system/src/Grav/Framework/Cache/Adapter/FileCache.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\Cache
  *
diff --git a/system/src/Grav/Framework/Cache/Adapter/MemoryCache.php b/system/src/Grav/Framework/Cache/Adapter/MemoryCache.php
index 84911fbe1..63e37a97d 100644
--- a/system/src/Grav/Framework/Cache/Adapter/MemoryCache.php
+++ b/system/src/Grav/Framework/Cache/Adapter/MemoryCache.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\Cache
  *
diff --git a/system/src/Grav/Framework/Cache/Adapter/SessionCache.php b/system/src/Grav/Framework/Cache/Adapter/SessionCache.php
index b1e9e9e51..0f0b497a0 100644
--- a/system/src/Grav/Framework/Cache/Adapter/SessionCache.php
+++ b/system/src/Grav/Framework/Cache/Adapter/SessionCache.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\Cache
  *
@@ -66,7 +67,7 @@ class SessionCache extends AbstractCache
 
     protected function doGetStored($key)
     {
-        $stored = isset($_SESSION[$this->getNamespace()][$key]) ? $_SESSION[$this->getNamespace()][$key] : null;
+        $stored = $_SESSION[$this->getNamespace()][$key] ?? null;
 
         if (isset($stored[self::LIFETIME]) && $stored[self::LIFETIME] < time()) {
             unset($_SESSION[$this->getNamespace()][$key]);
diff --git a/system/src/Grav/Framework/Cache/CacheInterface.php b/system/src/Grav/Framework/Cache/CacheInterface.php
index 54af40c69..f72c5d7eb 100644
--- a/system/src/Grav/Framework/Cache/CacheInterface.php
+++ b/system/src/Grav/Framework/Cache/CacheInterface.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\Cache
  *
diff --git a/system/src/Grav/Framework/Cache/CacheTrait.php b/system/src/Grav/Framework/Cache/CacheTrait.php
index 2f2b178ba..55879c126 100644
--- a/system/src/Grav/Framework/Cache/CacheTrait.php
+++ b/system/src/Grav/Framework/Cache/CacheTrait.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\Cache
  *
@@ -120,11 +121,11 @@ trait CacheTrait
     {
         if ($keys instanceof \Traversable) {
             $keys = iterator_to_array($keys, false);
-        } elseif (!is_array($keys)) {
+        } elseif (!\is_array($keys)) {
             throw new InvalidArgumentException(
                 sprintf(
                     'Cache keys must be array or Traversable, "%s" given',
-                    is_object($keys) ? get_class($keys) : gettype($keys)
+                    \is_object($keys) ? \get_class($keys) : \gettype($keys)
                 )
             );
         }
@@ -164,7 +165,7 @@ trait CacheTrait
             throw new InvalidArgumentException(
                 sprintf(
                     'Cache values must be array or Traversable, "%s" given',
-                    is_object($values) ? get_class($values) : gettype($values)
+                    \is_object($values) ? \get_class($values) : \gettype($values)
                 )
             );
         }
@@ -195,7 +196,7 @@ trait CacheTrait
             throw new InvalidArgumentException(
                 sprintf(
                     'Cache keys must be array or Traversable, "%s" given',
-                    is_object($keys) ? get_class($keys) : gettype($keys)
+                    \is_object($keys) ? \get_class($keys) : \gettype($keys)
                 )
             );
         }
@@ -283,20 +284,20 @@ trait CacheTrait
      */
     protected function validateKey($key)
     {
-        if (!is_string($key)) {
+        if (!\is_string($key)) {
             throw new InvalidArgumentException(
                 sprintf(
                     'Cache key must be string, "%s" given',
-                    is_object($key) ? get_class($key) : gettype($key)
+                    \is_object($key) ? \get_class($key) : \gettype($key)
                 )
             );
         }
         if (!isset($key[0])) {
             throw new InvalidArgumentException('Cache key length must be greater than zero');
         }
-        if (strlen($key) > 64) {
+        if (\strlen($key) > 64) {
             throw new InvalidArgumentException(
-                sprintf('Cache key length must be less than 65 characters, key had %s characters', strlen($key))
+                sprintf('Cache key length must be less than 65 characters, key had %s characters', \strlen($key))
             );
         }
         if (strpbrk($key, '{}()/\@:') !== false) {
@@ -332,7 +333,7 @@ trait CacheTrait
             return $this->getDefaultLifetime();
         }
 
-        if (is_int($ttl)) {
+        if (\is_int($ttl)) {
             return $ttl;
         }
 
diff --git a/system/src/Grav/Framework/Cache/Exception/CacheException.php b/system/src/Grav/Framework/Cache/Exception/CacheException.php
index 71caff7f6..5fae9ef32 100644
--- a/system/src/Grav/Framework/Cache/Exception/CacheException.php
+++ b/system/src/Grav/Framework/Cache/Exception/CacheException.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\Cache
  *
diff --git a/system/src/Grav/Framework/Cache/Exception/InvalidArgumentException.php b/system/src/Grav/Framework/Cache/Exception/InvalidArgumentException.php
index a00199b79..ce88d8d1a 100644
--- a/system/src/Grav/Framework/Cache/Exception/InvalidArgumentException.php
+++ b/system/src/Grav/Framework/Cache/Exception/InvalidArgumentException.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\Cache
  *
diff --git a/system/src/Grav/Framework/Collection/AbstractFileCollection.php b/system/src/Grav/Framework/Collection/AbstractFileCollection.php
index e2aa29cc2..9f6408e7d 100644
--- a/system/src/Grav/Framework/Collection/AbstractFileCollection.php
+++ b/system/src/Grav/Framework/Collection/AbstractFileCollection.php
@@ -95,7 +95,7 @@ class AbstractFileCollection extends AbstractLazyCollection implements FileColle
         if ($orderings = $criteria->getOrderings()) {
             $next = null;
             foreach (array_reverse($orderings) as $field => $ordering) {
-                $next = ClosureExpressionVisitor::sortByField($field, $ordering == Criteria::DESC ? -1 : 1, $next);
+                $next = ClosureExpressionVisitor::sortByField($field, $ordering === Criteria::DESC ? -1 : 1, $next);
             }
 
             uasort($filtered, $next);
@@ -107,7 +107,7 @@ class AbstractFileCollection extends AbstractLazyCollection implements FileColle
         $length = $criteria->getMaxResults();
 
         if ($offset || $length) {
-            $filtered = array_slice($filtered, (int)$offset, $length);
+            $filtered = \array_slice($filtered, (int)$offset, $length);
         }
 
         return new ArrayCollection($filtered);
diff --git a/system/src/Grav/Framework/ContentBlock/ContentBlock.php b/system/src/Grav/Framework/ContentBlock/ContentBlock.php
index 672dba4cc..ea24f4017 100644
--- a/system/src/Grav/Framework/ContentBlock/ContentBlock.php
+++ b/system/src/Grav/Framework/ContentBlock/ContentBlock.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\ContentBlock
  *
@@ -104,7 +105,7 @@ class ContentBlock implements ContentBlockInterface
         }
 
         $array = [
-            '_type' => get_class($this),
+            '_type' => \get_class($this),
             '_version' => $this->version,
             'id' => $this->id
         ];
@@ -163,8 +164,8 @@ class ContentBlock implements ContentBlockInterface
     {
         $this->checkVersion($serialized);
 
-        $this->id = isset($serialized['id']) ? $serialized['id'] : $this->generateId();
-        $this->checksum = isset($serialized['checksum']) ? $serialized['checksum'] : null;
+        $this->id = $serialized['id'] ?? $this->generateId();
+        $this->checksum = $serialized['checksum'] ?? null;
 
         if (isset($serialized['content'])) {
             $this->setContent($serialized['content']);
diff --git a/system/src/Grav/Framework/ContentBlock/ContentBlockInterface.php b/system/src/Grav/Framework/ContentBlock/ContentBlockInterface.php
index fff8f2e73..45f4c29c1 100644
--- a/system/src/Grav/Framework/ContentBlock/ContentBlockInterface.php
+++ b/system/src/Grav/Framework/ContentBlock/ContentBlockInterface.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\ContentBlock
  *
diff --git a/system/src/Grav/Framework/ContentBlock/HtmlBlock.php b/system/src/Grav/Framework/ContentBlock/HtmlBlock.php
index 3fd345b8c..f7916aea3 100644
--- a/system/src/Grav/Framework/ContentBlock/HtmlBlock.php
+++ b/system/src/Grav/Framework/ContentBlock/HtmlBlock.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\ContentBlock
  *
@@ -131,7 +132,7 @@ class HtmlBlock extends ContentBlock implements HtmlBlockInterface
      */
     public function addStyle($element, $priority = 0, $location = 'head')
     {
-        if (!is_array($element)) {
+        if (!\is_array($element)) {
             $element = ['href' => (string) $element];
         }
         if (empty($element['href'])) {
@@ -175,7 +176,7 @@ class HtmlBlock extends ContentBlock implements HtmlBlockInterface
      */
     public function addInlineStyle($element, $priority = 0, $location = 'head')
     {
-        if (!is_array($element)) {
+        if (!\is_array($element)) {
             $element = ['content' => (string) $element];
         }
         if (empty($element['content'])) {
@@ -206,7 +207,7 @@ class HtmlBlock extends ContentBlock implements HtmlBlockInterface
      */
     public function addScript($element, $priority = 0, $location = 'head')
     {
-        if (!is_array($element)) {
+        if (!\is_array($element)) {
             $element = ['src' => (string) $element];
         }
         if (empty($element['src'])) {
@@ -243,7 +244,7 @@ class HtmlBlock extends ContentBlock implements HtmlBlockInterface
      */
     public function addInlineScript($element, $priority = 0, $location = 'head')
     {
-        if (!is_array($element)) {
+        if (!\is_array($element)) {
             $element = ['content' => (string) $element];
         }
         if (empty($element['content'])) {
@@ -274,7 +275,7 @@ class HtmlBlock extends ContentBlock implements HtmlBlockInterface
      */
     public function addHtml($html, $priority = 0, $location = 'bottom')
     {
-        if (empty($html) || !is_string($html)) {
+        if (empty($html) || !\is_string($html)) {
             return false;
         }
         if (!isset($this->html[$location])) {
@@ -302,7 +303,7 @@ class HtmlBlock extends ContentBlock implements HtmlBlockInterface
         ];
 
         foreach ($this->blocks as $block) {
-            if ($block instanceof HtmlBlock) {
+            if ($block instanceof self) {
                 $blockAssets = $block->getAssetsFast();
                 $assets['frameworks'] += $blockAssets['frameworks'];
 
diff --git a/system/src/Grav/Framework/ContentBlock/HtmlBlockInterface.php b/system/src/Grav/Framework/ContentBlock/HtmlBlockInterface.php
index 204e199e5..37eea0cd7 100644
--- a/system/src/Grav/Framework/ContentBlock/HtmlBlockInterface.php
+++ b/system/src/Grav/Framework/ContentBlock/HtmlBlockInterface.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\ContentBlock
  *
diff --git a/system/src/Grav/Framework/File/AbstractFile.php b/system/src/Grav/Framework/File/AbstractFile.php
index ab819cbcf..99e57a603 100644
--- a/system/src/Grav/Framework/File/AbstractFile.php
+++ b/system/src/Grav/Framework/File/AbstractFile.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  * @package    Grav\Framework\File
  *
@@ -8,7 +11,9 @@
 
 namespace Grav\Framework\File;
 
-class AbstractFile
+use Grav\Framework\File\Interfaces\FileInterface;
+
+class AbstractFile implements FileInterface
 {
     /** @var string */
     private $filepath;
@@ -58,7 +63,7 @@ class AbstractFile
      *
      * @return string
      */
-    public function getFilePath()
+    public function getFilePath() : string
     {
         return $this->filepath;
     }
@@ -68,7 +73,7 @@ class AbstractFile
      *
      * @return string
      */
-    public function getPath()
+    public function getPath() : string
     {
         if (null === $this->path) {
             $this->setPathInfo();
@@ -82,7 +87,7 @@ class AbstractFile
      *
      * @return string
      */
-    public function getFilename()
+    public function getFilename() : string
     {
         if (null === $this->filename) {
             $this->setPathInfo();
@@ -96,7 +101,7 @@ class AbstractFile
      *
      * @return string
      */
-    public function getBasename()
+    public function getBasename() : string
     {
         if (null === $this->basename) {
             $this->setPathInfo();
@@ -111,7 +116,7 @@ class AbstractFile
      * @param $withDot
      * @return string
      */
-    public function getExtension($withDot = false)
+    public function getExtension($withDot = false) : string
     {
         if (null === $this->extension) {
             $this->setPathInfo();
@@ -125,7 +130,7 @@ class AbstractFile
      *
      * @return bool
      */
-    public function exists()
+    public function exists() : bool
     {
         return is_file($this->filepath);
     }
@@ -157,7 +162,7 @@ class AbstractFile
      * @return bool
      * @throws \RuntimeException
      */
-    public function lock($block = true)
+    public function lock($block = true) : bool
     {
         if (!$this->handle) {
             if (!$this->mkdir($this->getPath())) {
@@ -179,7 +184,7 @@ class AbstractFile
      *
      * @return bool
      */
-    public function unlock()
+    public function unlock() : bool
     {
         if (!$this->handle) {
             return false;
@@ -199,7 +204,7 @@ class AbstractFile
      *
      * @return bool True = locked, false = not locked.
      */
-    public function isLocked()
+    public function isLocked() : bool
     {
         return $this->locked;
     }
@@ -209,7 +214,7 @@ class AbstractFile
      *
      * @return bool
      */
-    public function isWritable()
+    public function isWritable() : bool
     {
         return is_writable($this->filepath) || $this->isWritableDir($this->getPath());
     }
@@ -261,7 +266,7 @@ class AbstractFile
      * @param string $path
      * @return bool
      */
-    public function rename($path)
+    public function rename($path) : bool
     {
         if ($this->exists() && !@rename($this->filepath, $path)) {
             return false;
@@ -277,7 +282,7 @@ class AbstractFile
      *
      * @return bool
      */
-    public function delete()
+    public function delete() : bool
     {
         return @unlink($this->filepath);
     }
@@ -288,7 +293,7 @@ class AbstractFile
      * @throws \RuntimeException
      * @internal
      */
-    protected function mkdir($dir)
+    protected function mkdir($dir) : bool
     {
         // Silence error for open_basedir; should fail in mkdir instead.
         if (!@is_dir($dir)) {
@@ -309,7 +314,7 @@ class AbstractFile
      * @return bool
      * @internal
      */
-    protected function isWritableDir($dir)
+    protected function isWritableDir($dir) : bool
     {
         if ($dir && !file_exists($dir)) {
             return $this->isWritableDir(dirname($dir));
@@ -318,7 +323,7 @@ class AbstractFile
         return $dir && is_dir($dir) && is_writable($dir);
     }
 
-    protected function setFilepath($filepath)
+    protected function setFilepath($filepath) : void
     {
         $this->filepath = $filepath;
         $this->filename = null;
@@ -327,7 +332,7 @@ class AbstractFile
         $this->extension = null;
     }
 
-    protected function setPathInfo()
+    protected function setPathInfo() : void
     {
         $pathInfo = static::pathinfo($this->filepath);
         $this->filename = $pathInfo['filename'];
diff --git a/system/src/Grav/Framework/File/DataFile.php b/system/src/Grav/Framework/File/DataFile.php
index db773c4dd..e1250652b 100644
--- a/system/src/Grav/Framework/File/DataFile.php
+++ b/system/src/Grav/Framework/File/DataFile.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  * @package    Grav\Framework\File
  *
@@ -51,7 +54,7 @@ class DataFile extends AbstractFile
      */
     public function save($data)
     {
-        if (is_string($data)) {
+        if (\is_string($data)) {
             try {
                 $this->formatter->decode($data);
             } catch (\RuntimeException $e) {
diff --git a/system/src/Grav/Framework/File/File.php b/system/src/Grav/Framework/File/File.php
index 60e556b8a..bcac43941 100644
--- a/system/src/Grav/Framework/File/File.php
+++ b/system/src/Grav/Framework/File/File.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  * @package    Grav\Framework\File
  *
diff --git a/system/src/Grav/Framework/File/Formatter/FormatterInterface.php b/system/src/Grav/Framework/File/Formatter/FormatterInterface.php
index 273bf7873..1149eb23e 100644
--- a/system/src/Grav/Framework/File/Formatter/FormatterInterface.php
+++ b/system/src/Grav/Framework/File/Formatter/FormatterInterface.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\File\Formatter
  *
diff --git a/system/src/Grav/Framework/File/Formatter/IniFormatter.php b/system/src/Grav/Framework/File/Formatter/IniFormatter.php
index 45be61012..1f1cb4478 100644
--- a/system/src/Grav/Framework/File/Formatter/IniFormatter.php
+++ b/system/src/Grav/Framework/File/Formatter/IniFormatter.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\File\Formatter
  *
diff --git a/system/src/Grav/Framework/File/Formatter/JsonFormatter.php b/system/src/Grav/Framework/File/Formatter/JsonFormatter.php
index 4a2d2fac4..ad185096e 100644
--- a/system/src/Grav/Framework/File/Formatter/JsonFormatter.php
+++ b/system/src/Grav/Framework/File/Formatter/JsonFormatter.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\File\Formatter
  *
diff --git a/system/src/Grav/Framework/File/Formatter/MarkdownFormatter.php b/system/src/Grav/Framework/File/Formatter/MarkdownFormatter.php
index 415f7ceb0..8fb6c7e84 100644
--- a/system/src/Grav/Framework/File/Formatter/MarkdownFormatter.php
+++ b/system/src/Grav/Framework/File/Formatter/MarkdownFormatter.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\File\Formatter
  *
diff --git a/system/src/Grav/Framework/File/Formatter/SerializeFormatter.php b/system/src/Grav/Framework/File/Formatter/SerializeFormatter.php
index 88302180b..7f506e9c4 100644
--- a/system/src/Grav/Framework/File/Formatter/SerializeFormatter.php
+++ b/system/src/Grav/Framework/File/Formatter/SerializeFormatter.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\File\Formatter
  *
@@ -84,9 +85,9 @@ class SerializeFormatter implements FormatterInterface
      */
     protected function preserveLines($data, $search, $replace)
     {
-        if (is_string($data)) {
+        if (\is_string($data)) {
             $data = str_replace($search, $replace, $data);
-        } elseif (is_array($data)) {
+        } elseif (\is_array($data)) {
             foreach ($data as &$value) {
                 $value = $this->preserveLines($value, $search, $replace);
             }
diff --git a/system/src/Grav/Framework/File/Formatter/YamlFormatter.php b/system/src/Grav/Framework/File/Formatter/YamlFormatter.php
index d59f9e7d4..53652c2b9 100644
--- a/system/src/Grav/Framework/File/Formatter/YamlFormatter.php
+++ b/system/src/Grav/Framework/File/Formatter/YamlFormatter.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\File\Formatter
  *
@@ -80,7 +81,7 @@ class YamlFormatter implements FormatterInterface
     public function decode($data)
     {
         // Try native PECL YAML PHP extension first if available.
-        if ($this->config['native'] && function_exists('yaml_parse')) {
+        if (\function_exists('yaml_parse') && $this->config['native']) {
             // Safely decode YAML.
             $saved = @ini_get('yaml.decode_php');
             @ini_set('yaml.decode_php', 0);
diff --git a/system/src/Grav/Framework/File/IniFile.php b/system/src/Grav/Framework/File/IniFile.php
index 2b3dadbc4..6a81a1751 100644
--- a/system/src/Grav/Framework/File/IniFile.php
+++ b/system/src/Grav/Framework/File/IniFile.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  * @package    Grav\Framework\File
  *
diff --git a/system/src/Grav/Framework/File/Interfaces/FileInterface.php b/system/src/Grav/Framework/File/Interfaces/FileInterface.php
new file mode 100644
index 000000000..3bf023a74
--- /dev/null
+++ b/system/src/Grav/Framework/File/Interfaces/FileInterface.php
@@ -0,0 +1,153 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * @package    Grav\Framework\File
+ *
+ * @copyright  Copyright (C) 2015 - 2018 Trilby Media, LLC. All rights reserved.
+ * @license    MIT License; see LICENSE file for details.
+ */
+
+namespace Grav\Framework\File\Interfaces;
+
+interface FileInterface
+{
+    public function __construct($filepath);
+
+    /**
+     * Unlock file when the object gets destroyed.
+     */
+    public function __destruct();
+
+    /**
+     * Get full path to the file.
+     *
+     * @return string
+     */
+    public function getFilePath() : string;
+
+    /**
+     * Get path to the file.
+     *
+     * @return string
+     */
+    public function getPath() : string;
+
+    /**
+     * Get filename.
+     *
+     * @return string
+     */
+    public function getFilename() : string;
+
+    /**
+     * Return name of the file without extension.
+     *
+     * @return string
+     */
+    public function getBasename() : string;
+
+    /**
+     * Return file extension.
+     *
+     * @param $withDot
+     * @return string
+     */
+    public function getExtension($withDot = false) : string;
+
+    /**
+     * Check if file exits.
+     *
+     * @return bool
+     */
+    public function exists() : bool;
+
+    /**
+     * Return file modification time.
+     *
+     * @return int|bool Timestamp or false if file doesn't exist.
+     */
+    public function getCreationTime();
+
+    /**
+     * Return file modification time.
+     *
+     * @return int|bool Timestamp or false if file doesn't exist.
+     */
+    public function getModificationTime();
+
+    /**
+     * Lock file for writing. You need to manually unlock().
+     *
+     * @param bool $block  For non-blocking lock, set the parameter to false.
+     * @return bool
+     * @throws \RuntimeException
+     */
+    public function lock($block = true) : bool;
+
+    /**
+     * Unlock file.
+     *
+     * @return bool
+     */
+    public function unlock() : bool;
+
+    /**
+     * Returns true if file has been locked for writing.
+     *
+     * @return bool True = locked, false = not locked.
+     */
+    public function isLocked() : bool;
+
+    /**
+     * Check if file can be written.
+     *
+     * @return bool
+     */
+    public function isWritable() : bool;
+
+    /**
+     * (Re)Load a file and return RAW file contents.
+     *
+     * @return string
+     */
+    public function load();
+
+    /**
+     * Save file.
+     *
+     * @param  mixed $data
+     * @throws \RuntimeException
+     */
+    public function save($data);
+
+    /**
+     * Rename file in the filesystem if it exists.
+     *
+     * @param string $path
+     * @return bool
+     */
+    public function rename($path) : bool;
+
+    /**
+     * Delete file from filesystem.
+     *
+     * @return bool
+     */
+    public function delete() : bool;
+
+    /**
+     * Multi-byte-safe pathinfo replacement.
+     * Replacement for pathinfo(), but stream, multibyte and cross-platform safe.
+     *
+     * @see    http://www.php.net/manual/en/function.pathinfo.php
+     *
+     * @param string     $path    A filename or path, does not need to exist as a file
+     * @param int|string $options Either a PATHINFO_* constant,
+     *                            or a string name to return only the specified piece
+     *
+     * @return string|array
+     */
+    public static function pathinfo($path, $options = null);
+}
diff --git a/system/src/Grav/Framework/File/JsonFile.php b/system/src/Grav/Framework/File/JsonFile.php
index cc9dbb4dd..ca63f88ac 100644
--- a/system/src/Grav/Framework/File/JsonFile.php
+++ b/system/src/Grav/Framework/File/JsonFile.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  * @package    Grav\Framework\File
  *
diff --git a/system/src/Grav/Framework/File/MarkdownFile.php b/system/src/Grav/Framework/File/MarkdownFile.php
index c8dac7dd6..69d9a0de7 100644
--- a/system/src/Grav/Framework/File/MarkdownFile.php
+++ b/system/src/Grav/Framework/File/MarkdownFile.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  * @package    Grav\Framework\File
  *
diff --git a/system/src/Grav/Framework/File/YamlFile.php b/system/src/Grav/Framework/File/YamlFile.php
index e19dfa726..65f009818 100644
--- a/system/src/Grav/Framework/File/YamlFile.php
+++ b/system/src/Grav/Framework/File/YamlFile.php
@@ -1,4 +1,7 @@
 <?php
+
+declare(strict_types=1);
+
 /**
  * @package    Grav\Framework\File
  *
diff --git a/system/src/Grav/Framework/Media/Interfaces/MediaCollectionInterface.php b/system/src/Grav/Framework/Media/Interfaces/MediaCollectionInterface.php
index ed7dea907..6c865493e 100644
--- a/system/src/Grav/Framework/Media/Interfaces/MediaCollectionInterface.php
+++ b/system/src/Grav/Framework/Media/Interfaces/MediaCollectionInterface.php
@@ -1,4 +1,12 @@
 <?php
+
+/**
+ * @package    Grav\Framework\Media
+ *
+ * @copyright  Copyright (C) 2015 - 2018 Trilby Media, LLC. All rights reserved.
+ * @license    MIT License; see LICENSE file for details.
+ */
+
 namespace Grav\Framework\Media\Interfaces;
 
 /**
diff --git a/system/src/Grav/Framework/Media/Interfaces/MediaInterface.php b/system/src/Grav/Framework/Media/Interfaces/MediaInterface.php
index 48dbc688f..444ce4343 100644
--- a/system/src/Grav/Framework/Media/Interfaces/MediaInterface.php
+++ b/system/src/Grav/Framework/Media/Interfaces/MediaInterface.php
@@ -1,4 +1,12 @@
 <?php
+
+/**
+ * @package    Grav\Framework\Media
+ *
+ * @copyright  Copyright (C) 2015 - 2018 Trilby Media, LLC. All rights reserved.
+ * @license    MIT License; see LICENSE file for details.
+ */
+
 namespace Grav\Framework\Media\Interfaces;
 
 /**
diff --git a/system/src/Grav/Framework/Media/Interfaces/MediaManipulationInterface.php b/system/src/Grav/Framework/Media/Interfaces/MediaManipulationInterface.php
index e48bacbac..54202672d 100644
--- a/system/src/Grav/Framework/Media/Interfaces/MediaManipulationInterface.php
+++ b/system/src/Grav/Framework/Media/Interfaces/MediaManipulationInterface.php
@@ -2,6 +2,13 @@
 
 declare(strict_types=1);
 
+/**
+ * @package    Grav\Framework\Media
+ *
+ * @copyright  Copyright (C) 2015 - 2018 Trilby Media, LLC. All rights reserved.
+ * @license    MIT License; see LICENSE file for details.
+ */
+
 namespace Grav\Framework\Media\Interfaces;
 
 use Grav\Common\Media\Interfaces\MediaInterface;
diff --git a/system/src/Grav/Framework/Media/Interfaces/MediaObjectInterface.php b/system/src/Grav/Framework/Media/Interfaces/MediaObjectInterface.php
index 71e54544c..dc64145df 100644
--- a/system/src/Grav/Framework/Media/Interfaces/MediaObjectInterface.php
+++ b/system/src/Grav/Framework/Media/Interfaces/MediaObjectInterface.php
@@ -1,4 +1,12 @@
 <?php
+
+/**
+ * @package    Grav\Framework\Media
+ *
+ * @copyright  Copyright (C) 2015 - 2018 Trilby Media, LLC. All rights reserved.
+ * @license    MIT License; see LICENSE file for details.
+ */
+
 namespace Grav\Framework\Media\Interfaces;
 
 /**
diff --git a/system/src/Grav/Framework/Object/Access/NestedPropertyTrait.php b/system/src/Grav/Framework/Object/Access/NestedPropertyTrait.php
index 0a173c49c..7ae6a36a8 100644
--- a/system/src/Grav/Framework/Object/Access/NestedPropertyTrait.php
+++ b/system/src/Grav/Framework/Object/Access/NestedPropertyTrait.php
@@ -58,9 +58,9 @@ trait NestedPropertyTrait
 
             $offset = array_shift($path);
 
-            if ((is_array($current) || is_a($current, 'ArrayAccess')) && isset($current[$offset])) {
+            if ((\is_array($current) || is_a($current, 'ArrayAccess')) && isset($current[$offset])) {
                 $current = $current[$offset];
-            } elseif (is_object($current) && isset($current->{$offset})) {
+            } elseif (\is_object($current) && isset($current->{$offset})) {
                 $current = $current->{$offset};
             } else {
                 return $default;
@@ -98,7 +98,7 @@ trait NestedPropertyTrait
             // Handle arrays and scalars.
             if ($current === null) {
                 $current = [$offset => []];
-            } elseif (is_array($current)) {
+            } elseif (\is_array($current)) {
                 if (!isset($current[$offset])) {
                     $current[$offset] = [];
                 }
@@ -142,7 +142,7 @@ trait NestedPropertyTrait
             if ($current === null) {
                 return $this;
             }
-            if (is_array($current)) {
+            if (\is_array($current)) {
                 if (!isset($current[$offset])) {
                     return $this;
                 }
diff --git a/system/src/Grav/Framework/Object/Base/ObjectCollectionTrait.php b/system/src/Grav/Framework/Object/Base/ObjectCollectionTrait.php
index d3bc3792a..2fbf3faeb 100644
--- a/system/src/Grav/Framework/Object/Base/ObjectCollectionTrait.php
+++ b/system/src/Grav/Framework/Object/Base/ObjectCollectionTrait.php
@@ -30,7 +30,7 @@ trait ObjectCollectionTrait
     {
         $list = [];
         foreach ($this->getIterator() as $key => $value) {
-            $list[$key] = is_object($value) ? clone $value : $value;
+            $list[$key] = \is_object($value) ? clone $value : $value;
         }
 
         return $this->createFrom($list);
@@ -132,7 +132,7 @@ trait ObjectCollectionTrait
 
         foreach ($this->getIterator() as $id => $element) {
             $list[$id] = method_exists($element, $method)
-                ? call_user_func_array([$element, $method], $arguments) : null;
+                ? \call_user_func_array([$element, $method], $arguments) : null;
         }
 
         return $list;
diff --git a/system/src/Grav/Framework/Object/Base/ObjectTrait.php b/system/src/Grav/Framework/Object/Base/ObjectTrait.php
index 67a5bf5b5..c4dfaa293 100644
--- a/system/src/Grav/Framework/Object/Base/ObjectTrait.php
+++ b/system/src/Grav/Framework/Object/Base/ObjectTrait.php
@@ -44,7 +44,7 @@ trait ObjectTrait
             return $type . static::$type;
         }
 
-        $class = get_class($this);
+        $class = \get_class($this);
         return $type . strtolower(substr($class, strrpos($class, '\\') + 1));
     }
 
diff --git a/system/src/Grav/Framework/Object/Collection/ObjectExpressionVisitor.php b/system/src/Grav/Framework/Object/Collection/ObjectExpressionVisitor.php
index 80d5cee77..775da50b1 100644
--- a/system/src/Grav/Framework/Object/Collection/ObjectExpressionVisitor.php
+++ b/system/src/Grav/Framework/Object/Collection/ObjectExpressionVisitor.php
@@ -101,7 +101,7 @@ class ObjectExpressionVisitor extends ClosureExpressionVisitor
     public static function sortByField($name, $orientation = 1, \Closure $next = null)
     {
         if (!$next) {
-            $next = function() {
+            $next = function($a, $b) {
                 return 0;
             };
         }
@@ -175,7 +175,7 @@ class ObjectExpressionVisitor extends ClosureExpressionVisitor
             case Comparison::MEMBER_OF:
                 return function ($object) use ($field, $value) {
                     $fieldValues = static::getObjectFieldValue($object, $field);
-                    if (!is_array($fieldValues)) {
+                    if (!\is_array($fieldValues)) {
                         $fieldValues = iterator_to_array($fieldValues);
                     }
                     return \in_array($value, $fieldValues, true);
diff --git a/system/src/Grav/Framework/Object/Property/ObjectPropertyTrait.php b/system/src/Grav/Framework/Object/Property/ObjectPropertyTrait.php
index 6dcd7f42f..920630739 100644
--- a/system/src/Grav/Framework/Object/Property/ObjectPropertyTrait.php
+++ b/system/src/Grav/Framework/Object/Property/ObjectPropertyTrait.php
@@ -111,7 +111,7 @@ trait ObjectPropertyTrait
             if ($doCreate === true) {
                 $this->_definedProperties[$property] = true;
                 $this->{$property} = null;
-            } elseif (is_callable($doCreate)) {
+            } elseif (\is_callable($doCreate)) {
                 $this->_definedProperties[$property] = true;
                 $this->{$property} = $this->offsetLoad($property, $doCreate());
             } else {
@@ -153,7 +153,7 @@ trait ObjectPropertyTrait
     protected function initObjectProperties()
     {
         $this->_definedProperties = [];
-        foreach (get_object_vars($this) as $property => $value) {
+        foreach (\get_object_vars($this) as $property => $value) {
             if ($property[0] !== '_') {
                 $this->_definedProperties[$property] = ($value !== null);
             }
diff --git a/system/src/Grav/Framework/Psr7/AbstractUri.php b/system/src/Grav/Framework/Psr7/AbstractUri.php
index 5ddda9bf4..d0c4cc085 100644
--- a/system/src/Grav/Framework/Psr7/AbstractUri.php
+++ b/system/src/Grav/Framework/Psr7/AbstractUri.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\Psr7
  *
@@ -156,10 +157,10 @@ abstract class AbstractUri implements UriInterface
      * @inheritdoc
      * @throws \InvalidArgumentException
      */
-    public function withUserInfo($user, $password = '')
+    public function withUserInfo($user, $password = null)
     {
         $user = UriPartsFilter::filterUserInfo($user);
-        $password = UriPartsFilter::filterUserInfo($password);
+        $password = UriPartsFilter::filterUserInfo($password ?? '');
 
         if ($this->user === $user && $this->password === $password) {
             return $this;
diff --git a/system/src/Grav/Framework/Route/Route.php b/system/src/Grav/Framework/Route/Route.php
index 63f6f7ec3..9492b0c01 100644
--- a/system/src/Grav/Framework/Route/Route.php
+++ b/system/src/Grav/Framework/Route/Route.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\Route
  *
@@ -101,7 +102,7 @@ class Route
         $parts = explode('/', $this->route);
 
         if ($offset !== 0 || $length !== null) {
-            $parts = array_slice($parts, $offset, $length);
+            $parts = \array_slice($parts, $offset, $length);
         }
 
         return $parts;
@@ -159,7 +160,7 @@ class Route
      */
     public function getGravParam($param)
     {
-        return isset($this->gravParams[$param]) ? $this->gravParams[$param] : null;
+        return $this->gravParams[$param] ?? null;
     }
 
     /**
@@ -168,7 +169,7 @@ class Route
      */
     public function getQueryParam($param)
     {
-        return isset($this->queryParams[$param]) ? $this->queryParams[$param] : null;
+        return $this->queryParams[$param] ?? null;
     }
 
     /**
@@ -221,7 +222,7 @@ class Route
      */
     protected function withParam($type, $param, $value)
     {
-        $oldValue = isset($this->{$type}[$param]) ? $this->{$type}[$param] : null;
+        $oldValue = $this->{$type}[$param] ?? null;
 
         if ($oldValue === $value) {
             return $this;
@@ -284,7 +285,7 @@ class Route
             $this->root = RouteFactory::getRoot();
             $this->language = RouteFactory::getLanguage();
 
-            $path = isset($parts['path']) ? $parts['path'] : '/';
+            $path = $parts['path'] ?? '/';
             if (isset($parts['params'])) {
                 $this->route = trim(rawurldecode($path), '/');
                 $this->gravParams = $parts['params'];
diff --git a/system/src/Grav/Framework/Route/RouteFactory.php b/system/src/Grav/Framework/Route/RouteFactory.php
index 830d7c75c..6890043c4 100644
--- a/system/src/Grav/Framework/Route/RouteFactory.php
+++ b/system/src/Grav/Framework/Route/RouteFactory.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\Route
  *
@@ -108,7 +109,7 @@ class RouteFactory
             return $path;
         }
 
-        $path = dirname(substr($path, 0, $pos));
+        $path = \dirname(substr($path, 0, $pos));
         if ($path === '.') {
             return '';
         }
@@ -122,7 +123,7 @@ class RouteFactory
      */
     public static function getParams($path)
     {
-        $params = ltrim(substr($path, strlen(static::stripParams($path))), '/');
+        $params = ltrim(substr($path, \strlen(static::stripParams($path))), '/');
 
         return $params !== '' ? static::parseParams($params) : [];
     }
diff --git a/system/src/Grav/Framework/Session/Session.php b/system/src/Grav/Framework/Session/Session.php
index 3c2a417e1..4643cb4f2 100644
--- a/system/src/Grav/Framework/Session/Session.php
+++ b/system/src/Grav/Framework/Session/Session.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\Session
  *
@@ -158,7 +159,7 @@ class Session implements SessionInterface
         ];
 
         foreach ($options as $key => $value) {
-            if (is_array($value)) {
+            if (\is_array($value)) {
                 // Allow nested options.
                 foreach ($value as $key2 => $value2) {
                     $ckey = "{$key}.{$key2}";
@@ -293,7 +294,7 @@ class Session implements SessionInterface
      */
     public function __get($name)
     {
-        return isset($_SESSION[$name]) ? $_SESSION[$name] : null;
+        return $_SESSION[$name] ?? null;
     }
 
     /**
@@ -328,8 +329,8 @@ class Session implements SessionInterface
      */
     protected function ini_set($key, $value)
     {
-        if (!is_string($value)) {
-            if (is_bool($value)) {
+        if (!\is_string($value)) {
+            if (\is_bool($value)) {
                 $value = $value ? '1' : '0';
             }
             $value = (string)$value;
diff --git a/system/src/Grav/Framework/Session/SessionInterface.php b/system/src/Grav/Framework/Session/SessionInterface.php
index 74c5f2aca..be3462015 100644
--- a/system/src/Grav/Framework/Session/SessionInterface.php
+++ b/system/src/Grav/Framework/Session/SessionInterface.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\Session
  *
diff --git a/system/src/Grav/Framework/Uri/Uri.php b/system/src/Grav/Framework/Uri/Uri.php
index 2821360af..501e070ab 100644
--- a/system/src/Grav/Framework/Uri/Uri.php
+++ b/system/src/Grav/Framework/Uri/Uri.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\Uri
  *
@@ -81,7 +82,7 @@ class Uri extends AbstractUri
     {
         $queryParams = $this->getQueryParams();
 
-        return isset($queryParams[$key]) ? $queryParams[$key] : null;
+        return $queryParams[$key] ?? null;
     }
 
     /**
diff --git a/system/src/Grav/Framework/Uri/UriFactory.php b/system/src/Grav/Framework/Uri/UriFactory.php
index c6bd4289d..15bf0cbdd 100644
--- a/system/src/Grav/Framework/Uri/UriFactory.php
+++ b/system/src/Grav/Framework/Uri/UriFactory.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\Uri
  *
@@ -57,13 +58,13 @@ class UriFactory
         if (isset($env['REQUEST_SCHEME'])) {
             $scheme = strtolower($env['REQUEST_SCHEME']);
         } else {
-            $https = isset($env['HTTPS']) ? $env['HTTPS'] : '';
+            $https = $env['HTTPS'] ?? '';
             $scheme = (empty($https) || strtolower($https) === 'off') ? 'http' : 'https';
         }
 
         // Build user and password.
-        $user = isset($env['PHP_AUTH_USER']) ? $env['PHP_AUTH_USER'] : '';
-        $pass = isset($env['PHP_AUTH_PW']) ? $env['PHP_AUTH_PW'] : '';
+        $user = $env['PHP_AUTH_USER'] ?? '';
+        $pass = $env['PHP_AUTH_PW'] ?? '';
 
         // Build host.
         $host = 'localhost';
@@ -79,11 +80,11 @@ class UriFactory
         $port = isset($env['SERVER_PORT']) ? (int)$env['SERVER_PORT'] : null;
 
         // Build path.
-        $request_uri = isset($env['REQUEST_URI']) ? $env['REQUEST_URI'] : '';
+        $request_uri = $env['REQUEST_URI'] ?? '';
         $path = parse_url('http://example.com' . $request_uri, PHP_URL_PATH);
 
         // Build query string.
-        $query = isset($env['QUERY_STRING']) ? $env['QUERY_STRING'] : '';
+        $query = $env['QUERY_STRING'] ?? '';
         if ($query === '') {
             $query = parse_url('http://example.com' . $request_uri, PHP_URL_QUERY);
         }
@@ -115,7 +116,7 @@ class UriFactory
      */
     public static function parseUrl($url)
     {
-        if (!is_string($url)) {
+        if (!\is_string($url)) {
             throw new \InvalidArgumentException('URL must be a string');
         }
 
diff --git a/system/src/Grav/Framework/Uri/UriPartsFilter.php b/system/src/Grav/Framework/Uri/UriPartsFilter.php
index 36efa16cb..cce15513f 100644
--- a/system/src/Grav/Framework/Uri/UriPartsFilter.php
+++ b/system/src/Grav/Framework/Uri/UriPartsFilter.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @package    Grav\Framework\Uri
  *
@@ -23,7 +24,7 @@ class UriPartsFilter
      */
     public static function filterScheme($scheme)
     {
-        if (!is_string($scheme)) {
+        if (!\is_string($scheme)) {
             throw new \InvalidArgumentException('Uri scheme must be a string');
         }
 
@@ -39,7 +40,7 @@ class UriPartsFilter
      */
     public static function filterUserInfo($info)
     {
-        if (!is_string($info)) {
+        if (!\is_string($info)) {
             throw new \InvalidArgumentException('Uri user info must be a string');
         }
 
@@ -59,7 +60,7 @@ class UriPartsFilter
      */
     public static function filterHost($host)
     {
-        if (!is_string($host)) {
+        if (!\is_string($host)) {
             throw new \InvalidArgumentException('Uri host must be a string');
         }
 
@@ -83,7 +84,7 @@ class UriPartsFilter
      */
     public static function filterPort($port = null)
     {
-        if (null === $port || (is_int($port) && ($port >= 1 && $port <= 65535))) {
+        if (null === $port || (\is_int($port) && ($port >= 1 && $port <= 65535))) {
             return $port;
         }
 
@@ -103,7 +104,7 @@ class UriPartsFilter
      */
     public static function filterPath($path)
     {
-        if (!is_string($path)) {
+        if (!\is_string($path)) {
             throw new \InvalidArgumentException('Uri path must be a string');
         }
 
@@ -125,7 +126,7 @@ class UriPartsFilter
      */
     public static function filterQueryOrFragment($query)
     {
-        if (!is_string($query)) {
+        if (!\is_string($query)) {
             throw new \InvalidArgumentException('Uri query string and fragment must be a string');
         }